Plant Molecular Biology 73: 67-87 (2010)
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Cross-species approaches to seed dormancy and germination: conservation and biodiversity of ABA-regulated mechanisms and the Brassicaceae DOG1 genes
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Kai Graeber • Ada Linkies • Kerstin Müller • Andrea Wunchova • Anita Rott • Gerhard Leubner-Metzger
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Botany / Plant Physiology, Institute for Biology II, Faculty of Biology, University of Freiburg, Schänzlestr. 1, D-79104 Freiburg, Germany, Web: 'The Seed Biology Place' http://www.seedbiology.de (K.G., A.L., K.M., A.R., G.L.-M.)
Department of Cell Biology and Genetics, Palacky University in Olomouc, Slechtitelu 11, 78371 Olomouc-Holice, Czech Republic, and Department of Botany and Plant Physiology, Mendel University of Agriculture and Forestry in Brno, Zemedelska 1, 61300 Brno, Czech Republic (A.W.)
Received August 28, 2009; Accepted November 22, 2009; Published online: December 15, 2009
DOI: 10.1007/s11103-009-9583-x
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Abstract. Seed dormancy is genetically determined with substantial environmental influence mediated, at least in part, by the plant hormone abscisic acid (ABA). The ABA-related transcription factor ABI3/VP1 (ABA INSENSITIVE3 / VIVIPAROUS1) is widespread among green plants. Alternative splicing of its transcripts appears to be involved in regulating seed dormancy, but the role of ABI3/VP1 goes beyond seeds and dormancy. In contrast, DOG1 (DELAY OF GERMINATION 1), a major quantitative trait gene more specifically involved in seed dormancy, was so far only known from Arabidopsis thaliana (AtDOG1) and whether it also has roles during the germination of non-dormant seeds was not known. Seed germination of Lepidium sativum ('garden cress') is controlled by ABA and its antagonists gibberellins and ethylene and involves the production of apoplastic hydroxyl radicals. We found orthologs of AtDOG1 in the Brassicaceae relatives L. sativum (LesaDOG1) and Brassica rapa (BrDOG1) and compared their gene structure and the sequences of their transcripts expressed in seeds. Tissue-specific analysis of LesaDOG1 transcript levels in L. sativum seeds showed that they are degraded upon imbibition in the radicle and the micropylar endosperm. ABA inhibits germination in that it delays radicle protrusion and endosperm weakening and it increased LesaDOG1 transcript levels during early germination due to enhanced transcription and/or inhibited degradation. A reduced decrease in LesaDOG1 transcript levels upon ABA treatment is evident in the late germination phase in both tissues. This temporal and ABA-related transcript expression pattern suggests a role for LesaDOG1 in the control of germination timing of non-dormant L. sativum seeds. The possible involvement of the ABA-related transcription factors ABI3 and ABI5 in the regulation of DOG1 transcript expression is discussed. Other species of the monophyletic genus Lepidium showed coat or embryo dormancy and are therefore highly suited for comparative seed biology.
Key words: ABI3/VP1 transcription factor, coat and embryo dormancy, comparative Brassicaceae seed biology, Delay of Germination 1 (DOG1), endosperm weakening, ethylene-ABA antagonism, reactive oxygen species, seed biomechanics
Financial support: Our work is funded by grants of the Deutsche Forschungsgemeinschaft (grant no. DFG LE720/6 and LE720/7) and the Deutscher Akademischer Austauschdienst (grant no. DAAD D/0628197) to G.L.-M., and the Wissenschaftliche Gesellschaft Freiburg to G.L.-M. and A.L..
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